Method of producing a piezoelectric/electrostrictive device

ABSTRACT

A method of producing a piezoelectric/electrostrictive device in which a piezoelectric/electrostrictive element including a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces. The first and second surfaces are inclined at given angles to one of the narrower and wider surfaces. The laminate includes piezoelectric/electrostrictive layers and interposed internal electrodes, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers. A first external electrode is formed on the first surface of the laminate and is coupled to the first group internal electrodes. A second external electrode is formed on the second surface of the laminate and is coupled to the second group internal electrodes.

CROSS REFERNECE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/631,293,filed Jul. 31, 2003, now allowed, which is a continuation of U.S.application Ser. No. 09/918,274, filed Jul. 30, 2001, now abandoned, theentireties of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to apiezoelectric/electrostrictive element, a piezoelectric/electrostrictivedevice and a production method thereof, and more particularly to alaminated piezoelectric/electrostrictive element and a laminatedpiezoelectric/electrostrictive device made up ofpiezoelectric/electrostrictive layers and internal electrode layerslaminated alternately, and a production method thereof.

BACKGROUND OF THE INVENTION

In recent years, a variety of fields such as optics, magnetic recording,precision machining, and printing demand a displacement element forcontrolling, for example, the length or position of an optical path inthe order of a submicron or vibrations precisely. As such a displacementelement meeting the above demand, there is one employing displacementprovided by a reverse piezoelectric effect or an electrostrictive effecttaken place when the voltage is applied to apiezoelectric/electrostrictive material made of, for example, aferroelectric substance.

Conventionally, as such a displacement element, a laminatedpiezoelectric element 100, as shown in FIG. 34, which is disclosed inJapanese Patent First Publication No. 4-309274 is known. Thepiezoelectric/electrostrictive element 100 includes, as shown in FIG.34, a lamination 104 formed by laminating a plurality of piezoelectricceramic layers 101 and electrode layers 102 alternately and a pair ofelectrically insulated external electrodes 104 and 105 which connect theelectrode layers 102 alternately on opposed side surfaces of thelaminate 103 and are so formed as to extend to upper and lower surfacesof the laminate 103. In the laminated piezoelectric element 100, ridgesdefined by the side surfaces and the upper and lower surfaces of thelaminate 103 are rounded to an extent where the radius of curvature ofthe ridges exceeds half the thickness of the piezoelectric ceramiclayers 101.

The production of the laminated piezoelectric element 100 shown in FIG.34 is accomplished by first weighing and grinding raw material, mixingit with binder, and defoaming the mixture, after which the mixture isshaped into a sheet from which rectangular green sheets 101A are punched(which will be the piezoelectric ceramic layers 101 by baking). Aconductive paste is printed over a given area of one surface of thegreen sheet 101A to form the electrode layer 102. Next, the green sheets101A on which the electrode layers 102 are printed properly are, asshown in FIG. 35, laminated and bonded by pressure and cut as neededafter which it is baked to produce the laminate 103 as shown in FIG. 36.As a result, the green sheets 101A are, as mentioned above, baked toproduce the piezoelectric ceramic layers 101. In the laminate 103,arrangement positions of the electrode layers 102 are predetermined on apair of opposed side surfaces thereof so that the electrode layers 102may be exposed alternately. Afterwards, on given areas of upper andlower surfaces of the thus produced laminate 103, an external uppersurface electrode 104A, and an external lower surface electrode 105A areformed. Next, on a pair of opposed side surfaces 106 and 107 to whichthe electrode layers 102 of the laminate 103 are exposed alternately,external side surface electrodes (thick film electrodes) 104B and 105Bare formed to make the laminated piezoelectric element 100 shown in FIG.34. The external side surface electrode 104B is so formed as to connectwith the external upper surface electrode 104A, while the external sidesurface electrode 105B is so formed as to connect with the externallower surface electrode 105A. As a method of forming the above-mentionedexternal electrodes 104 and 105, there is a dipping method or anevaporation method.

FIG. 37 shows an actuator 200 utilizing the thus constructed laminatedpiezoelectric element 100. The actuator 200 has the laminatedpiezoelectric element 100 secured on a movable plate (diaphragm) 110 byan adhesive 111.

As another displacement element, a piezoelectric displacement element,as disclosed in Japanese Patent First Publication No. 63-295269, isknown which is equipped with a plurality of opposed inner electrodelayers in a ceramic thin plate exhibiting the piezoelectric effect.Comers that are boundaries of side surfaces and upper and lower surfacesof the ceramic thin plate are chamfered mechanically. On front andreverse surfaces and the opposed side surfaces of the ceramic thinplate, a pair of opposed surface electrodes connecting with internalelectrode layers is so formed that the electrodes are electricallyinsulated from each other. The opposed surface electrodes are formed onthe surfaces of the ceramic thin plate by a physical vapor depositionmethod such as a sputtering method or a vapor deposition method or afilm forming method such as plating.

SUMMARY OF THE INVENTION

The laminated piezoelectric element 100, as shown in FIG. 34, hasproblems in that the possibility that edges of the green sheets 101A(shown in FIG. 35) are deformed, damaged, or broken by handling is high.Particularly, a thin piezoelectric element in which a total filmthickness (thickness) of the laminate 103 is 100 μm or less has a highpossibility that the green sheets 101A are broken by handling. Theconventional laminated piezoelectric element 100, thus, has a problemthat the fabrication yield is low.

The piezoelectric displacement element, as disclosed in Japanese PatentFirst Publication No. 63-295269 is chamfered by mechanically cutting endportions of the ceramic thin film diagonally, which results in anincrease in production processes. The mechanical cutting may also causedamage to the ceramic thin film.

The invention was made in order to solve the above problems. It is,thus, an object of the invention to provide apiezoelectric/electrostrictive element and apiezoelectric/electrostrictive device which are excellent in strength,shock resistance, handling, dimensional accuracy, positional accuracy,stability of element characteristics, and fabrication yield, and toprovide a production method thereof.

In order to solve the above problems, the first feature of the inventionlies in a piezoelectric/electrostrictive element including asubstantially trapezoidal laminate having narrower and wider surfaceslying substantially in parallel to each other and first and secondsurfaces opposed to each other between the narrower and wider surfaces.The first and second surfaces are inclined at given angles with respectto one of the narrower and wider surfaces. The trapezoidal laminate ismade up of a plurality of piezoelectric/electrostrictive layers and aplurality of internal electrodes, each of which is disposed between anadjacent two of the piezoelectric/electrostrictive layers. The internalelectrodes are divided into a first and a second group, each of thefirst group internal electrodes lying over one of the second groupinternal electrodes through one of the piezoelectric/electrostrictivelayers. A first external electrode is formed on the first surface of thelaminate, and is coupled to the first group internal electrodes; and asecond external electrode formed on the second surface of said laminate,said second external electrodes being coupled to the second groupinternal electrodes.

The thus constructed piezoelectric/electrostrictive element is of asubstantially trapezoidal shape which decreases in width from one of thebottom surfaces to the other bottom surface, so that the angle which theslant surfaces of both sides make with the other bottom surface isobtuse, thus resulting in an increase in strength of a ridge portion (acorner) defined by the other bottom surface and the slant surfaces.Therefore, for example, when the other (narrower) bottom surface issecured on a movable plate (diaphragm), the breakage or damage of theridge portion caused by an external force or vibrations of thepiezoelectric/electrostrictive element itself is avoided. When the otherbottom surface of the piezoelectric/electrostrictive element is securedon the movable plate (diaphragm) by adhesive, a recess-shaped (V-grooveshaped) gap defined by the movable plate and the slant surfaces of boththe sides of the piezoelectric/electrostrictive element can be filledwith the adhesive, thereby resulting in a further increase in force(bonding strength) which secures the piezoelectric/electrostrictiveelement to the movable plate. The existence of the adhesive in therecess-shaped gap offers the effect of avoiding removal of thepiezoelectric/electrostrictive element from the movable plate even ifthe stress arising from a difference in thermal expansion between thepiezoelectric/electrostrictive element and the movable plate isproduced.

The piezoelectric/electrostrictive layers are decreased in widthgradually in one of the directions of lamination. Thus, for example,when the external electrode layers, the piezoelectric/electrostrictivelayers, and the internal electrode layers are laminated in a givenorder, it is possible to pile up the piezoelectric/electrostrictivelayers on a backing layer stably. Therefore, when the external electrodelayers, the piezoelectric/electrostrictive layers, and the internalelectrode layers are laminated by printing using, for example, a screenprinting method, the printing is achieved easily since a lower one ofthe piezoelectric/electrostrictive layers has an area greater than thatof an upper one of the piezoelectric/electrostrictive layers. The screenprinting method makes it possible to apply, for example, via aconductive paste, the external electrode layers to the slant surface (aside surface portion) of the laminate.

Both the external electrode layers formed on the side surface portionsextend along the wider surface of said laminate, thereby ensuring ajoint area (a pad portion) which establishes a joint of wires forapplying a drive voltage to the external electrode layers or wires fordetecting a produced voltage, which facilitates connection of the wires.Particularly, as described above, when the narrower bottom surface ofthe laminate is secured on the movable plate, it is possible to bond thewires on a sufficient area of the wider bottom surface. The width of oneof the external electrode layers extending on the wider bottom surfaceof the laminate is greater, thereby allowing the one of the externalelectrode layers to be used as a voltage applying electrode or a voltagedetecting electrode.

Additionally, one of the surfaces of the piezoelectric/electrostrictiveelement may be formed by a piezoelectric/electrostrictive layer toincrease a bonding strength using adhesive has the affinity to thepiezoelectric/electrostrictive layers, for example, when the side of thepiezoelectric/electrostrictive layer is bonded to the movable plate.

The second feature of the invention lies in apiezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces. The firstand second surfaces are inclined at given angles with respect to one ofthe narrower and wider surfaces. The trapezoidal laminate is made up ofa plurality of piezoelectric/electrostrictive layers and a plurality ofinternal electrodes, each of which is disposed between an adjacent twoof the piezoelectric/electrostrictive layers. The internal electrodesare divided into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layersfirst external electrode is formed on the first surface of the laminate,and is coupled to the first group internal electrodes. A second externalelectrode is formed on the second surface of said laminate, and iscoupled to the second group internal electrodes. Thepiezoelectric/electrostrictive element is bonded to a surface of amovable plate on a side of the narrower surface of the laminate.

In the piezoelectric/electrostrictive device, the narrower bottomsurface of the laminate is bonded to the surface of the movable plate,so that a corner portion having an obtuse angle defined by the narrowerbottom surface and both side surface portions engages the movable plate.The corner having the obtuse angle will have strength greater than acorner having an acute angle or a right angle and offers the effect ofincreasing the durability such as the strength or shock resistance ofthe piezoelectric/electrostrictive device.

A gap (recess) formed by both the side surface portions of thepiezoelectric/electrostrictive device and the movable plate defines aliquid sump of adhesive having flowability prior to solidification andworks to absorb an excess or a lack of the adhesive caused by avariation in quantity of the applied adhesive or undulations of themovable plate and the piezoelectric/electrostrictive element. Theapplication of a proper quantity of the adhesive to a suitable area ofthe movable plate will enable automatic alignment of thepiezoelectric/electrostrictive element with a proper position with aidof an effect such as surface tension of the adhesive within the gap.

Additionally, filling the gap with the adhesive enables firminstallation of the piezoelectric/electrostrictive element on themovable plate. If the adhesive with which the gap is filled keeps theelasticity after being solidified, it alleviates the stress arising froma difference in thermal expansion between the movable plate and thepiezoelectric/electrostrictive element, thereby avoiding removable ofthe piezoelectric/electrostrictive element from the movable plate.Specifically, the filling of the gap defined by the side portions of thepiezoelectric/electrostrictive element and the movable plate with theadhesive will restrict a reduction in strength to fix thepiezoelectric/electrostrictive element even if thepiezoelectric/electrostrictive element is decreased in size.

Further, the external electrode layers formed on both the side surfaceportions of the piezoelectric/electrostrictive element extend on thewider bottom surface of the laminate, thus providing a joint areasufficient for establishing connection of external wires to the externalelectrode layers.

The movable plate is made of a conductive material. One of the externalelectrode layers of the piezoelectric/electrostrictive element isconnected to the movable plate, thereby increasing a wiring space of theother external electrode layer and facilitating ease of a connectingoperation.

The third feature of the invention lies in a method of producing apiezoelectric/electrostrictive element including the following steps:

-   -   a first step of preparing a ceramic substrate having a given        width;    -   a second step of forming a laminate on the ceramic substrate,        the laminate being made up of first and second portions laid to        overlap one another;    -   a third step of baking the ceramic substrate and the laminate at        a given temperature; and    -   a fourth step of removing the laminate from the ceramic        substrate;    -   the first portion of the laminate is formed using the following        steps:    -   printing a first electrode layer and a second electrode layer on        the ceramic substrate which are disposed at a given interval        away from one another;    -   forming a piezoelectric/electrostrictive layer using a        piezoelectric/electrostrictive paste on the first and second        electrode layers so as to cover portions of the first and second        electrode layers other than edge portions thereof lying outward        in a widthwise direction of the ceramic substrate; and    -   forming a first electrode layer on an upper surface and a side        surface of the piezoelectric/electrostrictive layer so as to        establish an electric connection only with the first electrode        layer lying immediately beneath the first electrode layer formed        in this step.

The second portion of the laminate is formed by performing the followingset of steps a given number of times which include:

-   -   forming a piezoelectric/electrostrictive layer using a        piezoelectric/electrostrictive paste on an uppermost one of the        first electrode layers, the piezoelectric/electrostrictive layer        formed in this step having a width smaller than that of the        piezoelectric/electrostrictive layer lying immediately beneath        the piezoelectric/electrostrictive layer formed in this step;    -   forming a second electrode layer on an upper surface and a side        surface of an uppermost one of the        piezoelectric/electrostrictive layers so as to establish an        electric connection only with the second electrode layer lying        immediately beneath the second electrode layer formed in this        step;    -   forming a piezoelectric/electrostrictive layer using a        piezoelectric/electrostrictive paste on an uppermost one of the        second electrode layers, the piezoelectric/electrostrictive        layer formed in this step having a width smaller than that of        the piezoelectric/electrostrictive layer lying immediately        beneath the piezoelectric/electrostrictive layer formed in this        step; and    -   forming a first electrode layer on an upper surface and a side        surface of an uppermost one of the        piezoelectric/electrostrictive layers so as to establish an        electric connection only with the first electrode layer lying        immediately beneath the first electrode layer formed in this        step.

In the method of producing the thus constructedpiezoelectric/electrostrictive element according to the third feature,it is possible to pile up the piezoelectric/electrostrictive layers byprinting so that areas thereof decrease gradually, thus resulting inease of manufacture. The piezoelectric/electrostrictive layers, thefirst electrode material layer, and the second electrode material layermay be formed using a printing method, thus allowing apiezoelectric/electrostrictive element to be produced which is higher indimensional accuracy, positional accuracy, less susceptible to adverseeffects, such shifting during transportation, and deformation caused bythe transportation, and eliminating the need for process of transportingand piling up the piezoelectric/electrostrictive layers, which avoidsbreakage or damage of the piezoelectric/electrostrictive layers causedby handling thereof.

The formation of portions which become continuous external side surfaceelectrodes on both sides of the laminate is achieved in sequence byrepeating printing of the first and second electrode material layers,thus eliminating the need for a process of forming additional externalside surface electrodes.

Further, a film which disappears upon baking of the laminate ispreformed on a ceramic substrate used in producing thepiezoelectric/electrostrictive element, thereby resulting in easyremoval of the piezoelectric/electrostrictive element from the ceramicsubstrate when baked.

In this invention, the external side surface electrode which defines anoutermost contour of the piezoelectric/electrostrictive element asviewed in a plane may be formed by printing with high positionalaccuracy. For example, when the piezoelectric/electrostrictive elementis positioned by positioning pins to mount thepiezoelectric/electrostrictive element on a movable plate, it ispossible to arrange the piezoelectric/electrostrictive element with highpositional accuracy.

The fourth feature of the invention lies in a method of producing apiezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to one another and first and second surfacesopposed to one another between the narrower and wider surfaces. Thefirst and second surfaces are inclined at given angles with respect toone of the narrower and wider surfaces. The trapezoidal laminate is madeup of a plurality of piezoelectric/electrostrictive layers and aplurality of internal electrodes, each of which is disposed between anadjacent two of the piezoelectric/electrostrictive layers. The internalelectrodes are broken up into a first and a second group, each of thefirst group internal electrodes lying over one of the second groupinternal electrodes through one of the piezoelectric/electrostrictivelayers. A first external electrode is formed on the first surface of thelaminate and is coupled to the first group internal electrodes. A secondexternal electrode is formed on the second surface of the laminate andis coupled to the second group internal electrodes. Thepiezoelectric/electrostrictive element is bonded to a surface of amovable plate by an adhesive.

In the method of producing the thus constructedpiezoelectric/electrostrictive device, the narrower bottom surface sideof the laminate is bonded to the movable plate through the adhesive,thus facilitating ease of filling a gap (recess) defined by slants ofboth side surfaces of the piezoelectric/electrostrictive element and themovable plate with the adhesive. This allows the gap to be filled withthe adhesive in quantity suitable for the size of the gap, thus ensuringthe bonding strength. When piezoelectric/electrostrictive elements arejoined to each other, gaps (recesses) are also formed by side surfaceportions of the piezoelectric/electrostrictive elements, thus offering asimilar effect of increasing the bonding strength.

The narrower bottom surface of the piezoelectric/electrostrictiveelement is bonded to the movable plate, so that angles which the sidesurface portions of the piezoelectric/electrostrictive element make withthe movable plate will be obtuse, thus providing the effect of avoidinglocal breakage or damage of the piezoelectric/electrostrictive element.The same is true for a case where piezoelectric/electrostrictiveelements are bonded at narrower bottom surfaces to one another.

Automatic positioning of the piezoelectric/electrostrictive element isachieved by setting a coefficient of viscosity of the adhesive appliedon the surface of the movable plate to a given value to enable thefilling with adhesive of the gaps (recesses) defined by the slants ofthe side surfaces of the piezoelectric/electrostrictive element and themovable plate.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fully understanding of the nature and objects of the invention,reference should be made to the following detailed description of apreferred mode of practicing the invention, read in connection with theaccompanying drawings in which:

FIG. 1 is a perspective view which shows apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 2 is a plan view of a piezoelectric/electrostrictive elementaccording to the first embodiment of the invention;

FIG. 3 is a bottom view of a piezoelectric/electrostrictive elementaccording to the first embodiment of the invention;

FIG. 4 is a cross-sectional elevation on section line A-A of FIG. 2;

FIG. 5 is a side view of a piezoelectric/electrostrictive deviceaccording to the first embodiment of the invention;

FIG. 6 is a plan view of a piezoelectric/electrostrictive deviceaccording to the first embodiment of the invention;

FIG. 7 is an explanatory side view which represents usage of apiezoelectric/electrostrictive device according to the first embodimentof the invention;

FIG. 8 is an explanatory side view which shows a modified embodiment 1of a piezoelectric/electrostrictive device according to the firstembodiment of the invention;

FIG. 9 is an explanatory side view which shows a modified embodiment 2of a piezoelectric/electrostrictive device according to the firstembodiment of the invention;

FIG. 10 is an explanatory side view which shows a modified embodiment 3of a piezoelectric/electrostrictive device according to the firstembodiment of the invention;

FIG. 11 is an explanatory side view which shows a modified embodiment 4of a piezoelectric/electrostrictive device according to the firstembodiment of the invention;

FIG. 12 is a plan view which illustrates a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 13 is a side view which illustrates a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 14 is a plan view which illustrates a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 15 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 16 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 17 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 18 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 19 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 20 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 21 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 22 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 23 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 24 is a process sectional view which shows a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

FIG. 25 is a side view of a piezoelectric/electrostrictive elementaccording to the second embodiment of the invention;

FIG. 26 is a plan view of a piezoelectric/electrostrictive elementaccording to the second embodiment of the invention;

FIG. 27 is a side view of a piezoelectric/electrostrictive deviceaccording to the second embodiment of the invention;

FIG. 28 is a plan view which represents a production method of apiezoelectric/electrostrictive device according to the second embodimentof the invention;

FIG. 29 is a plan view which represents a production method of apiezoelectric/electrostrictive device according to the second embodimentof the invention;

FIG. 30 is a plan view which illustrates a movable plate positioning jigused in a production method of a piezoelectric/electrostrictive deviceaccording to the second embodiment of the invention;

FIG. 31 is a side view which illustrates a movable plate positioning jigused in a production method of a piezoelectric/electrostrictive deviceaccording to the second embodiment of the invention;

FIG. 32 is a plan view which illustrates an element positioning jig usein a production method of a piezoelectric/electrostrictive deviceaccording to the second embodiment of the invention;

FIG. 33 is a side view which shows a combination of a movable platepositioning jig and an element positioning jig used in a productionmethod of a piezoelectric/electrostrictive device according to thesecond embodiment of the invention;

FIG. 34 is a perspective view which shows a conventionalpiezoelectric/electrostrictive element;

FIG. 35 is a perspective view which shows a production process of aconventional piezoelectric/electrostrictive element;

FIG. 36 is a perspective view which shows a laminate of a conventionalpiezoelectric/electrostrictive element;

FIG. 37 is a side view which shows a conventionalpiezoelectric/electrostrictive device;

FIG. 38 is an explanatory plan view which shows positioning of aconventional piezoelectric/electrostrictive element; and

FIG. 39 is an enlarged partial side view of a conventionalpiezoelectric/electrostrictive element.

DETAILED DESCRIPTION OF THE INVENTION

A piezoelectric/electrostrictive element, apiezoelectric/electrostrictive device, and a production method thereofwill be explained in detail with reference to embodiments as illustratedin the drawings. The attention should be paid to the fact that thedrawings are schematic, and the thickness and a film thickness ratio ofmaterial layers are different from those in actual use. Practicalthickness or dimensions should be decided with reference to thefollowing explanation. Of course, parts whose dimensional relation andratio are different from one another are included in the severaldrawings.

The piezoelectric/electrostrictive element and thepiezoelectric/electrostrictive device according to the inventionincludes an element which converts electric energy into mechanicalenergy, or vice versa by the reverse piezoelectric effect or theelectrostrictive effect, or the piezoelectric effect and a deviceequipped with the same. The piezoelectric/electrostrictive device of thepresent invention may be employed as passive elements such asacceleration sensors or impact sensors utilizing the piezoelectriceffect, as well as active elements such as a variety of actuators ortransducers, especially displacement elements using displacement by thereverse piezoelectric effect or the electrostrictive effect.

FIRST EMBODIMENT OF THE INVENTION

Piezoelectric/Electrostrictive Element

First, an outline of a structure of a piezoelectric/electrostrictiveelement of this embodiment will be described using FIGS. 1 to 4. Thepiezoelectric/electrostrictive element 10 of this embodiment, as shownin FIG. 1, includes, for example, four piezoelectric/electrostrictivelayers 11A, 11B, 11C, and 11D, for example, three internal electrodelayers 12A, 12B, and 12C interposed between an adjacent two of thepiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D. A pair ofexternal electrode layers 14 and 15 connect the internal electrodelayers 12A, 12B, and 12C in an alternate manner alternately. Thepiezoelectric/electrostrictive element 10 has a substantiallytrapezoidal laminated structure in which upper and lower opposed bottomsurfaces are both rectangular.

As shown in FIG. 1, an area of one of the bottom surfaces (uppersurface) f1 of the piezoelectric/electrostrictive element 10 is widerthan that of the other bottom surface (lower surface) f2. As shown inFIG. 1, the width of the wider bottom surface f1 (i.e., the length in anarrow direction as expressed by x in the drawing) is W1, and the lengththereof (i.e., the length in an arrow direction as expressed by y in thedrawing) is L1. FIG. 2 is a plan view which shows the wider bottomsurface f1. FIG. 3 is a bottom illustration of thepiezoelectric/electrostrictive element 10 as viewed from the narrowerbottom surface f2. As shown in FIG. 3, the width of the bottom surfacef2 is W2, which is smaller than the width W1 of the bottom surface f1.The length of the bottom surface f2 is equal to the length L1 of thebottom surface f1.

As can be seen from the bottom illustration of thepiezoelectric/electrostrictive element in FIG. 3, both side edges of thebottom surface f2 are located inward from both side edges of the bottomsurface f1 by the same distance W3 and overlap with the bottom surfacef1 in a lengthwise direction. The piezoelectric/electrostrictive element10, thus, has slant surfaces f3 and f4, as shown in FIGS. 1 and 3,formed on the sides thereof in the direction x. The pair of slantsurfaces f3 and f4 are inclined in a direction in which they approacheach other from the wider bottom surface f1 to the narrower bottomsurface f2.

The external structure of the piezoelectric/electrostrictive element 10has been explained above. Next, the structure and positional relation ofparts making up the piezoelectric/electrostrictive element 10 will beexplained in detail using FIGS. 1 to 4. FIG. 4 is a cross-sectional viewtaken along section line A-A shown in FIG. 2.

In the piezoelectric/electrostrictive element 10 according to thisembodiment, the piezoelectric/electrostrictive layers 11A, 11B, 11C, and11D are made of, for example, lead zirconium titanate (PZT). When formedby PZT, the strength of the piezoelectric/electrostrictive layers 11A,11B, 11C, and 11D is on the order of 70 MPa. The internal electrodelayers 12A, 12B, and 12C and the external electrode layers 14 and 15 aremade of, for example, platinum (Pt).

In the piezoelectric/electrostrictive element 10, thepiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D which arelaminated from the bottom surface f1 to the bottom surface f2 decreasein width gradually, so that the whole of thepiezoelectric/electrostrictive element 10 has, as mentioned above, theslant surfaces f3 and f4 formed on the side portions.

Between the piezoelectric/electrostrictive layers 11A and 11B, theinternal electrode layer 12A is disposed which extends from the slantsurface f3 toward the slant surface f4. The internal electrode 12A doesnot contact the slant surface f4. Between thepiezoelectric/electrostrictive layers 11B and 11C, the internalelectrode layer 12B is disposed which extends from the slant surface f4toward the slant surface f3. The internal electrode 12B does not contactthe slant surface f3. Between the piezoelectric/electrostrictive layers11C and 11D, the internal electrode layer 12C is disposed which extends,like the above described internal electrode layer 12A, from the slantsurface f3 toward the slant surface f4, and does not contact the slantsurface f4. It is advisable that the end edges of the above describedinternal electrodes 12A and 12C on the side of the slant surface f3 lieat the same location as viewed on a plane and overlap vertically,however, the internal electrode layer 12C may be shorter in the xdirection extending from the slant surface f3.

Further, slant portions 14A and 15A of the external electrode layers 14and 15 are formed on the slant surfaces f3 and f4. In this embodiment,the width of the slant portion 14A (i.e., the length in a direction ofslant surface inclination) is greater than that of the slant portion15A. The slant portion 14A is, as shown in FIG. 4, so formed as to coverthe whole of the slant surface f4, thereby establishing connection ofthe slant portion 14A of the external electrode layer 14 to the internalelectrode layer 12B. The slant surface portion 15A is formed toestablish a connection of the slant portion 15A of the externalelectrode layer 15 to the internal electrode layers 12A and 12C.Specifically, the external electrode layers 15 and 14 are so constructedas to connect with the internal electrode layers 12A, 12B, and 12Calternately.

On an upper surface (i.e., an outer surface) of the widestpiezoelectric/electrostrictive layer 11A, upper surface portions 14B and15B of the external electrode layers 14 and 15 are, as shown in FIGS. 1and 4, formed which extend from x-direction side edges of the outersurface of the piezoelectric/electrostrictive layer 11A so as toapproach one another. The upper surface portions 14B and 15B of theexternal electrode layers 14 and 15 are separate from one another on theside of one of the edge portions of the piezoelectric/electrostrictiveelement 10. Specifically, in this embodiment, the width (i.e., thelength in the x direction) of the upper surface portion 14B of theexternal electrode layer 14 is greater than the width of the externalelectrode layer 15. The edge of the upper surface portion 14B of theexternal electrode layer 14 on the side of the slant surface f3 lies atthe same location as that of the edge of the above described internalelectrode layer 12B as viewed on a plane, but however, it is not limitedto this location.

On a lower surface (i.e., an outer surface) of the narrowestpiezoelectric/electrostrictive layer 11D, the lower surface portion 14Cof the external electrode layer 14 is formed. The lower surface portion14C extends from a lower edge of the slant surface 14A toward the slantsurface f3. An edge of the lower surface portion 14C on the side of theslant surface f3 is set to lie at the same location as that of an edgeof the internal electrode layer 12B as viewed on a plane, however, it isnot limited to this location.

In this embodiment, the piezoelectric/electrostrictive layers 11A, 11B,11C, and 11D are four layers. The internal electrode layers 12A, 12B,and 12C are three layers. The upper surface portion 14B and the lowersurface portion 14C of the external electrode layer 14 are so arrangedon the upper and lower surfaces of the piezoelectric/electrostrictiveelement 10 as to function as opposed electrodes, however, the number ofthe layers and the number of the internal electrode layers connectingwith the external electrode layers 14 and 15, respectively, may be equalto or unequal number with respect to one another. The number of theelectrode layers are determined in terms of relations to a drive voltageand the degree of displacement of a movable plate, as will be describedlater. An increase in total number of the piezoelectric/electrostrictivelayers will cause a driving force driving the movable plate on which thepiezoelectric/electrostrictive element 10 is installed to be increased,thus enabling a greater displacement and result in an increase inrigidity of the piezoelectric/electrostrictive element 10, therebyincreasing the resonance frequency, which allows the speed of adisplacement operation to be increased easily.

As a practical material of the piezoelectric/electrostrictive layers11A, 11B, 11C, and 11D in this embodiment, ceramic may be used whichcontains one or a mixture of lead zirconate, lead titanate, leadmagnesium-niobate, lead nickel niobate, lead zinc niobate, leadmanganese niobate, lead antimony stannate, lead manganese tungstate,lead cobalt niobate, barium titanate, sodium bismuth titanate, kaliumsodium niobate, and strontium bismuth tantalate in addition to the abovedescribed lead zirconium titanate (PZT).

Particularly, material whose main components are lead zirconate, leadtitanate, and lead magnesium niobate or material whose main component issodium bismuth titanate have high electromechanical coupling factor andpiezoelectric constant, are low in reactivity to a firing setter (inthis case, ceramic oxide such as zirconia, alumina, or magnesia), andprovide stable compositions when the piezoelectric/electrostrictivelayers 11A, 11B, 11C, and 11D).

Further, one or some of oxides such as lanthanum (La), calcium (Ca),strontium (Sr), molybdenum (Mo), tungsten (W), barium (Ba), niobium(Nb), zinc (Zn), nickel (Ni), manganese (Mn), cerium (Ce), cadmium (Cd),chromium (Cr), cobalt (Co), antimony (Sb), iron (Fe), yttrium (Y),tantalum (Ta), lithium (Li), bismuth (Bi), and tin (Sn) may be mixedwith the above described ceramic material.

Additionally, for example, lanthanum (La) and strontium (Sr) may beadded to main components of lead zirconate, lead titanate, and leadmagnesium niobate for providing the advantage that it is possible toadjust the coercive electric field and piezoelectric characteristics.

The addition of an easy-to-vitrify material such as silica is preferablyavoided. The reason for this is that material such as silica reactseasily with a piezoelectric/electrostrictive material during heattreatment (i.e., firing) of the piezoelectric/electrostrictive layers11A, 11B, 11C, and 11D and change components thereof, thus resulting inthe deterioration of piezoelectric characteristics.

As the piezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D, theabove described variety of piezoelectric ceramics are preferably used,but electrostrictive ceramics, ferroelectric ceramics orantiferroelectric ceramics may be employed. However, in a case where thepiezoelectric/electrostrictive element 10 is used to position a magnetichead of a hard disc drive, the linearity to the amount of displacementof moving parts, a drive voltage, or an output voltage is important. Theuse of material that is smaller in electric-field strain hysteresis is,thus, preferable. Specifically, material having a coercive electricfield of 10 kV/mm or less is preferably used.

The external electrode layers 14 and 15 are preferably made of metalwhich is solid at room temperature and excellent in conductivity. Assuch a metal, in addition to the above described platinum (Pt), one ofaluminum (Al), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo),ruthenium (Ru), palladium (Pd), rhodium (Rh), silver (Ag), tin (Sn),tantalum (Ta), tungsten (W), iridium (Ir), gold (Au), and lead (Pb) oran alloy thereof may be used. A cermet material in which the samematerial as that of the piezoelectric/electrostrictive layers 11A, 11B,11C, and 11D is dispersed in the above materials may be used.

The selection of materials of the external electrode layers 14 and 15and the internal electrode layers 12A, 12B, and 12C of thepiezoelectric/electrostrictive element 10 is determined depending upon amethod of forming the piezoelectric/electrostrictive layers 11A, 11B,11C, and 11D. The method of forming the piezoelectric/electrostrictivelayers will be described later.

In the thus constructed piezoelectric/electrostrictive element 10,corners (ridge portions) 16 and 17 of both widthwise sides of the lowersurface f2, as shown in FIG. 4, have obtuse angles. Specifically, theangles which the lower surface f2 makes with the slant surfaces f3 andf4 are obtuse, so that the corners 16 and 17 have a greater strength ascompared with corners having right angles or acute angles. The increasein strength of the corners 16 and 17 serves to avoid the damage orbreakage of the corners 16 and 17 caused by an external force orvibrations of the piezoelectric/electrostrictive element 10 when thelower surface f2 of the piezoelectric/electrostrictive element 10 isinstalled on a movable plate (i.e., a diaphragm).

The upper surface portions 14B and 15B of the external electrode layers14 and 15 are both disposed on the side of the wider bottom surface f1,thus allowing the upper surface portions 14B and 15B to be used asconnection areas (i.e., pad portions), which facilitates connection ofwires.

Piezoelectric/Electrostrictive Device

Next, an embodiment of a piezoelectric/electrostrictive device 20employing the piezoelectric/electrostrictive element 10 according to thefirst embodiment will be described using FIGS. 5 to 7. FIG. 5 is a sideview of the piezoelectric/electrostrictive device 20. FIG. 6 is a planview of the piezoelectric/electrostrictive device 20.

The piezoelectric/electrostrictive device 20 is constructed to be of aunimorph type wherein the narrower lower surface f2 of the abovedescribed piezoelectric/electrostrictive element 10 is joined to amovable plate (diaphragm) 21 using adhesive 22. In thepiezoelectric/electrostrictive device 20 according to this embodiment,the piezoelectric/electrostrictive element 10 is substantially identicalin width (i.e., the length in ay direction, as expressed by an arrow inFIG. 6) with the movable plate 21. The length (i.e., the length in an xdirection, as expressed by an arrow in FIG. 6) of the movable plate 21is set longer than that of the piezoelectric/electrostrictive element10. The movable plate 21 may have flexibility and mechanical strengthwhich withstands breakage caused by bending. Material may be selected interms of the response and operationability.

In the piezoelectric/electrostrictive device 20, the adhesive 22 isinterposed between an upper surface of the movable plate 21 and a bottomsurface (lower surface) and the slant surfaces f3 and f4 of thepiezoelectric/electrostrictive element 10 to bond thepiezoelectric/electrostrictive element 10 on the upper surface of themovable plate 21. Particularly, V groove-shaped gaps defined between theslant surfaces f3 and f4 of the piezoelectric/electrostrictive element10 and the upper surface of the movable plate 21 are filled with theadhesive 22. As a result, the shape defined by thepiezoelectric/electrostrictive element 10 and the adhesive 22 will besubstantially trapezoidal or rectangular.

The movable plate 21 is a portion which operates based on driving of thepiezoelectric/electrostrictive element 10 and has a variety of partsinstalled thereon according to the purpose of use of thepiezoelectric/electrostrictive device 20. For instance, in a case wherethe piezoelectric/electrostrictive device 20 is used as a displacementelement, a shielding plate of an optical shutter etc. is installed. In acase where the piezoelectric/electrostrictive device 20 is employed toposition a magnetic head of a hard disc drive or in a ringing inhibitingmechanism, parts such as a magnetic head, a slider with the magnetichead, or a suspension with a slider which are required to be positionedare installed.

As material of the movable plate 21, ceramic including zirconia ispreferable. Particularly, material containing a main component ofstabilized zirconia or partially stabilized zirconia is desirable as thematerial of the movable plate 21 because it exhibits a greatermechanical strength and toughness if shaped to have a thin wall.

When the movable plate 21 is made of a metallic material, it ispreferably flexible or bendable. For example, as ferrous materials, avariety of stainless steels or a variety of spring steels are desirable.As non-ferrous materials, beryllium copper, phosphor bronze, nickel, ornickel-iron alloy is desirable.

In the thus constructed piezoelectric/electrostrictive device 20, the Vgroove-shaped gaps defined by the slant surfaces f3 and f4 and the uppersurface of the movable plate 21 are formed on both sides of thepiezoelectric/electrostrictive element 10 and work as a liquid sumps forthe adhesive 22 that is liquid or pastelike. The adhesive 22 held in thegaps is solidified while being kept lump by the surface tension, therebypreventing the adhesive 22 from overflowing to or around the upper sideof the piezoelectric/electrostrictive element 10 or the lower side ofthe movable plate 21. The V groove-shaped gaps defined by the slantsurfaces f3 and f4 of the piezoelectric/electrostrictive element 10 andthe upper surface of the movable plate 21 may be filled with theadhesive 22 in proper quantities by determining the quantity of theadhesive 22 to be applied to the movable plate 21 to a predeterminedvalue.

The side corners of the lower surface f2 of thepiezoelectric/electrostrictive element 10 both have, as described above,obtuse angles, and thus have a greater strength as compared with whenthey have right angles or acute angles. The increase in strength of thecorners 16 and 17 serves to avoid the damage or breakage of the corners16 and 17 caused by vibrations of the piezoelectric/electrostrictiveelement 10 or external forces.

Further, the stress arising from a thermal expansion difference betweenthe piezoelectric/electrostrictive element 10 and the movable plate 21is maximized near the ends of the piezoelectric/electrostrictive element10, but the adhesive 22 in the V groove-shaped gaps works to hold theadhesive strength and reduce the stress because of a low elasticity ofthe adhesive, thereby avoiding breakage and removal of the piezoelectricelement 10 from the movable plate 21.

The upper surface portions 14B and 15B of the external electrode layers14 and 15 are arranged on the side of the wider bottom surface f1 (i.e.,on the same plane), thereby facilitating connection of wire to the uppersurface portions 14B and 15B.

In a case where the thus constructed piezoelectric/electrostrictivedevice 20 is used as an active device, wires 23 and 24 may be connectedto the upper surface portion 14B of the external electrode layer 14 andthe upper surface portion 15B of the external electrode layer 15 formedon the bottom surface f1, respectively, and to a voltage applyingcircuit 25. Such an active device may be employed as transducers,actuators, frequency domain functional parts (filters), transformers,vibrators or resonators for communications or power sources,oscillators, or discriminators. The wires 23 and 24 are providedpreferably by a flexible printed circuit (FPC), flexible flat cables(FFC), or bonding wires.

In a case where the piezoelectric/electrostrictive device 20 is used asa passive device, the wires 23 and 24 may be connected to a voltagedetecting circuit 26 instead of the voltage applying circuit 25. In thecase where the wires 23 and 24 are joined to the upper surface portions14B and 15B of the external electrode layers 14 and 15 of thepiezoelectric/electrostrictive element 10, it is advisable that theadhesive 22 have electric insulation ability. Such a passive device maybe employed as ultrasonic sensors, acceleration sensors, angular ratesensors, shock sensors, or mass sensors.

Modified Embodiment 1 of Piezoelectric/Electrostrictive Device

FIG. 8 is an explanatory side view which illustrates the modifiedembodiment 1 of the piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive element 10 according to the firstembodiment. The structure of the modified embodiment 1 will be explainedwith the same reference numbers assigned to the same parts of themodified embodiment 1 as those of the above-describedpiezoelectric/electrostrictive device 20 and similar reference numbersassigned to similar parts thereof.

The piezoelectric/electrostrictive device 20A according to the modifiedembodiment 1 has the narrower bottom surface f2 of the above describedpiezoelectric/electrostrictive element 10 bonded and secured to theupper surface of the movable plate 21 having the conductivity using theadhesive 22 having the conductivity.

In the modified embodiment 1, the lower surface portion 14C and a lowerportion of the slant surface 14A of the external electrode layer 14formed on the bottom surface f2 of the piezoelectric/electrostrictiveelement 10 are joined to and secured on the movable plate 21 through theadhesive 22A. The adhesive 22A is set so as not to extend over the slantsurface 15A of the external electrode layer 15. This is achieved bydetermining the quantity of the adhesive 22A to be applied to themovable plate 21 properly.

In the thus constructed piezoelectric/electrostrictive device 20A, thewire 23 is joined to the movable plate 21, and the wire 24 is coupled tothe upper surface portion 15B of the external electrode layer 15. Theuse of the piezoelectric/electrostrictive device 20A as an active devicemay be achieved by connecting the wires 23 and 24, as shown in FIG. 8,to the voltage applying circuit 25. The use of thepiezoelectric/electrostrictive device 20A as a passive device may beachieved by connecting the wires 23 and 24, as shown in FIG. 8, to thevoltage detecting circuit 26.

As the adhesive 22 having the conductivity, a variety of conductivebonds including metallic fillers or anisotropic conductive bonds used inthe field of semiconductor packaging may be selected properly.

The movable plate 21 having the conductivity may be made of a metallicmaterial that is flexible or bendable. For example, as ferrousmaterials, a variety of stainless steels or a variety of spring steelsare desirable. As non-ferrous materials, beryllium copper, phosphorbronze, nickel, or nickel-iron alloy is desirable.

Modified Embodiment 2 of Piezoelectric/Electrostrictive Device

FIG. 9 is a side view which illustrates the modified embodiment 2 of thepiezoelectric/electrostrictive device using thepiezoelectric/electrostrictive elements 10 according to the firstembodiment. The structure of the modified embodiment 2 will be explainedwith the same reference numbers assigned to the same parts of themodified embodiment 2 as those of the above describedpiezoelectric/electrostrictive device 20 and similar reference numbersassigned to similar parts thereof.

The piezoelectric/electrostrictive device 20B according to the modifiedembodiment 2 has a bimorph type structure in which the above constructedpiezoelectric/electrostrictive element 10 is secured on each surface ofthe single movable plate 21 by the adhesive 22. The narrower bottomsurfaces f2 of the piezoelectric/electrostrictive elements 10 are placedin contact with the respective surfaces of the movable plate 21 andbonded so that the movable plate 21 is sandwiched therebetween.

In the piezoelectric/electrostrictive device 20B according to themodified embodiment 2, wires may be connected to the upper surfaceportions 14B and 15B of the external electrode layers 14 and 15 of eachof the piezoelectric/electrostrictive elements 10. Alternatively, themovable plate 21 may be used as a common electrode of thepiezoelectric/electrostrictive elements 10, and a wire may be connectedonly to the upper surface portion 15B of each of thepiezoelectric/electrostrictive element 10.

The assembly of the piezoelectric/electrostrictive elements 10 may be ofa symmetrical type (a series type) in which the directions ofpolarization are symmetrical with respect to the movable plate 21 or anasymmetrical type (a parallel type) in which the directions ofpolarization of the piezoelectric/electrostrictive elements 10 are thesame.

Modified Embodiment 3 of Piezoelectric/Electrostrictive Device

FIG. 10 is a side view which illustrates the modified embodiment 3 ofthe piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive elements 10 according to the firstembodiment. The structure of the modified embodiment 2 will be explainedusing the same reference numbers assigned to the same parts as those ofthe above described piezoelectric/electrostrictive device 20 and similarreference numbers assigned to similar parts.

In the piezoelectric/electrostrictive device 20C according to themodified embodiment 3, a pair of piezoelectric/electrostrictive elements10 are so arranged that the narrower bottom surfaces f2 thereof areopposed to each other and bonded to each other through the adhesive 22.The piezoelectric/electrostrictive device 20C has a bimorph typestructure which is not equipped with a movable plate.

In the modified embodiment 3, the assembly of thepiezoelectric/electrostrictive elements 10, like the above describedmodified embodiment 2, may be of the symmetrical type (the series type)or the asymmetrical type (the parallel type).

Modified Embodiment 4 of Piezoelectric/Electrostrictive Device

FIG. 11 is a side view which illustrates the modified embodiment 4 ofthe piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive elements 10 according to the firstembodiment.

The piezoelectric/electrostrictive device 20D according to the modifiedembodiment 4, as shown in FIG. 11, includes a base body 30 which hasmovable plate portions 31 and a fixing portion 32 formed integrally. Themovable plate portions 31 are opposed to each with through a given gap.The fixing portion 32 is interposed between the movable plate portions31 on the same side of ends of the movable plate portions 31. Thepiezoelectric/electrostrictive device 20D has thepiezoelectric/electrostrictive elements 10 bonded and secured to opposedoutside surfaces on the same side of end portions of the pair of movableplate portions 31.

The piezoelectric/electrostrictive device 20D has the structure in whichthe movable plate portions 31 are displaced by driving thepiezoelectric/electrostrictive elements 10, or the displacement of themovable plate portions 31 is detected by thepiezoelectric/electrostrictive elements 10. For instance, in thepiezoelectric/electrostrictive device 20D shown in FIG. 11, the movableplate portions 31 and the piezoelectric/electrostrictive elements 10constitute actuator portions 33. On the other ends of the movable plateportions 31, movable portions 34 are formed which are so formed as tohave thick walls projecting inwardly. The movable portions 34 aredisplaced following displacing operations of the movable plate portions31.

The base body 30 may be made of metal or ceramic as a whole or have ahybrid structure made of a combination of metal and ceramic. The basebody 30 may also have a structure in which respective parts are bondedby adhesive such as organic resin or glass, a ceramic one-piecestructure made of a fired ceramic green laminate, or a metallicone-piece structure formed integrally by brazing, soldering, eutecticbonding, or welding. It is advisable that the base body 30 be made of aceramic laminate formed integrally by firing a ceramic green laminate.Such ceramic one-piece members are of a structure which has highreliability of joints and is excellent in ensuring the rigidity and easyto manufacture.

The piezoelectric/electrostrictive elements 10 are bonded and secured tooutside surfaces on the same side of the end portions of the base body30 through the adhesive 22. The adhesive 22 may be an organic adhesiveor inorganic adhesive. The piezoelectric/electrostrictive elements 10are bonded at the narrower bottom surfaces f2 to the base body 30. The Vgroove-shaped gaps defined by the slant surfaces f3 and f4 of thepiezoelectric/electrostrictive elements 10 and the external surfaces ofthe base body 30 are filled with the adhesive 22. As a result, the shapedefined by the piezoelectric/electrostrictive elements 10 and theadhesive 22 will be substantially trapezoidal or rectangularparallelepipedic.

On the wider bottom surfaces f1 of the piezoelectric/electrostrictiveelements 10, the upper surface portions 14B of the external electrodelayers 14 and the upper surface portions 15B of the external electrodelayers 15 are disposed away from each other while keeping electricinsulation. A wire is, thus, bonded to the upper surface portions 14Band 15B which is to be joined to a voltage applying circuit or a voltagedetecting circuit which is not shown.

A gap (air), as shown in FIG. 11, may be defined between the opposed endsurfaces 34A of the pair of movable portions 34. Alternatively, aplurality of members made of material identical with or different fromthat of the movable portions 34 may be disposed between the opposed endsurfaces 34A.

In the thus constructed piezoelectric/electrostrictive device 20D, themovable portions 34, the movable plate portions 31, and the fixingportion 32 that define the basic structure are formed integrally by atough material. The piezoelectric/electrostrictive device 20D,therefore, has the advantages that it is higher in mechanical strength,excellent in handling, impact resistance, and moisture resistance, andless susceptible to harmful vibrations (e.g., residual vibrations ornoise during high-speed operation) as compared with apiezoelectric/electrostrictive device in which all parts are made of apiezoelectric/electrostrictive material that is fragile and relativelyheavy.

The formation of the gap between the opposed end surfaces 34A of themovable portions 34 of the piezoelectric/electrostrictive device 20Dprovides the flexibility of the movable portion 34 including one of theend surfaces 34A and the movable portion 34 including the other endsurface 34A, so that a deformation limit to which thepiezoelectric/electrostrictive device is not broken will be high. Thepiezoelectric/electrostrictive device 20D, therefore, has the advantagethat it is excellent in handling.

In the piezoelectric/electrostrictive device 20D, the movable portions34 are portions which operate, as described above, based on the amountof displacement of the movable plate portions 31 and have a variety ofparts installed thereon according to the purpose of use of thepiezoelectric/electrostrictive device 20D. For instance, in a case wherethe piezoelectric/electrostrictive device 20D is used as a displacementelement, for example, a shielding plate of an optical shutter isinstalled. In a case where the piezoelectric/electrostrictive device 20Dis employed to position a magnetic head of a hard disc drive or in aringing inhibiting mechanism, parts requiring positioning of themagnetic head, a slider with the magnetic head, or a suspension with aslider are installed.

The fixing portion 32 is, as described above, a portion supporting themovable plate portions 31 and the movable portions 34. For instance, ina case of use in positioning a magnetic head of a hard disc drive, thefixing portion 32 may be installed on a carriage arm mounted on a voicecoil motor (VCM), a mount plate attached to the carriage arm, or asuspension to fix the whole of the piezoelectric/electrostrictive device20D.

Further, in this modified embodiment, the movable plate portions 31 areportions driven by the displacement of thepiezoelectric/electrostrictive elements 10 and thus are thin plate likemembers having the flexibility and work to perform a function ofamplifying as a bending displacement an expansion/contractiondisplacement of the piezoelectric/electrostrictive elements 10 disposedon the surface thereof to transfer it to the movable portions 34.Therefore, the shape and material of the movable plate portions 31 whichonly exhibit the flexibility and mechanical strength less susceptible tobreakage caused by the bending displacement may be selected properly interms of response and operationability of the movable portions 34.

The movable plates 31 are preferably made of ceramics includingzirconia. Of the ceramics, material containing a main component ofstabilized zirconia and material containing a main component ofpartially stabilized zirconia are desirable in terms of a greatermechanical strength and a higher toughness even though a wall thicknessis small.

If the movable plate 31 is made of a metallic material, it is preferablyflexible or bendable. For example, as ferrous materials, a variety ofstainless steels or a variety of spring steels are desirable. Asnon-ferrous materials, beryllium copper, phosphor bronze, nickel, ornickel-iron alloy is desirable.

As the above described stabilized and partially stabilized zirconia, thefollowing stabilized or partially stabilized ones are preferable.Specifically, as compounds stabilizing or partially stabilizingzirconia, there are yttrium oxide, ytteribium oxide, cerium oxide,calcium oxide, and magnesium oxide. The desired stabilization ofzirconia may be achieved by adding at least one of the above compoundsor a mixture thereof to the zirconia.

Added amounts of yttrium oxide and ytteribium oxide are 1 to 30 mol %,preferably 1.5 to 10 mol %. An added amount of cerium oxide is 6 to 50mol %, preferably 8 to 20 mol %. Added amounts of calcium oxide andmagnesium oxide is 5 to 40 mol %, preferably 5 to 20 mol %. Of these,yttrium oxide is preferably used as a stabilizer. In the case whereyttrium oxide is used as a stabilizer, the amount thereof is preferably1.5 to 10 mol % and more preferably 2 to 4 mol %.

In order to obtain the mechanical strength and stabilized crystal phase,the mean crystal grain size is 0.05 to 3 μm, preferably 1 μm or less. Asdescribed above, the movable plate portion 31, like the movable portion34 and the fixing portion 32, may be made of ceramic. The use ofsubstantially the same material is advantageous to improve thereliability of joints and the strength of thepiezoelectric/electrostrictive device 20D and alleviate the complexityof manufacture.

Production Method of Piezoelectric/Electrostrictive Element of the FirstEmbodiment

Next, a production method of the piezoelectric/electrostrictive element10 according to the first embodiment will be described below using FIGS.12 to 24. The production method will be discussed while comparing andassociating new reference numbers of respective material layers withreference numbers of the piezoelectric/electrostrictive element 10 thatis a finished product as shown in FIGS. 1 to 4. The method includes thefollowing steps 1-12.

(1) First, a ceramic substrate 41, as shown in FIG. 12, is preparedwhich has a give size and is made of oxide such as zirconia, alumina, ormagnesia. The ceramic substrate 41 functions as a table for screenprinting and a firing substrate. Incidentally, the ceramic substrate 41measures approximately 40 mm×50 mm×0.3 mm.

(2) Carbon powder or a theobromine powder-dispersed paste is printedusing a 360 mesh metal screen having an emulsion film thickness of 10 μmon a row of areas on the ceramic substrate 41 which have a width greaterthan that of the piezoelectric/electrostrictive element 10 and thendried to form, as shown in FIG. 12, a row of disappearing films 42. Eachof the disappearing films 42 contains a plurality of element-formingareas in an x direction. FIG. 13 is a cross section on section line B-Bof FIG. 12. The disappearing films 42 will disappear by firing in asubsequent process to perform the function of facilitating removal ofthe piezoelectric/electrostrictive elements 10 from the ceramicsubstrate 41. A printing direction of the disappearing films 42 is adirection as illustrated by an arrow x in FIG. 12.

(3) Next, a platinum (Pt) paste is printed in a direction, as indicatedby arrow y in FIG. 14, using screens (printing plates) 43A, asillustrated by hatching, and dried. The screens 43A is set to 360 inmesh and 5 μm in emulsion film thickness. In this process, portionscorresponding to the upper surface portions 14B and 15B of the externalelectrode layers 14 and 15 of the piezoelectric/electrostrictive element10 of the first embodiment are printed. The use of the screen 43A, asillustrated by hatching in FIG. 14, enables simultaneous printing overthe plurality of element-forming areas along the x direction. FIG. 15shows Pt paste films 44 and 45 printed at an interval array from eachother using the screen 43A within one of the element-forming areas onthe disappearing film 42. An area including the Pt paste films 44 and 45and an intervening area is set to equal to that of a wider one of bottomsurfaces an unbaked preform of the piezoelectric/electrostrictiveelement 10. The screen 43A, as shown in FIG. 15, works to stick anemulsion film 47 to the metal screen 46 in a given pattern and transferplatinum pastes to the disappearing films 42 by pattern portions onwhich the emulsion layer 47 does not exist.

(4) Next, a piezoelectric paste is, as shown in FIG. 16, printed using ascreen 43B and dried to form an unbaked preform of a first one of thepiezoelectric/electrostrictive layers 11A. The screen 43B is provided byforming the emulsion layer 47 having a thickness of 25 μm in a givenpattern on the 360 mesh metal screen 46. A pattern of an opening of theemulsion layer 47 is determined to be slightly smaller than the abovedescribed area including the Pt paste films 44 and 45 and theintervening area therebetween. For details, the unbaked preform of thepiezoelectric/electrostrictive layer 11A printed by the screen 43B arelocated at both x-direction edges inside x-direction outside edges ofthe Pt paste films 44 and 45 by a distance x1. Both y-direction sideedges of the unbaked preform of the piezoelectric/electrostrictive layer11A overlap both y-direction side edges of each of the Pt paste films 44and 45.

(5) Next, a Pt paste film 48 is, as shown in FIG. 17, printed using ascreen 43C which will be a Pt film serving as the internal electrodelayer 12A and the slant surface portion 15A of the external electrodelayer 15 after firing and then dried. The Pt paste film 48 is laid tooverlap a given length L of the Pt paste film 44 in the x direction thatis formed in the above process through the unbaked preform of thepiezoelectric/electrostrictive layer 11A. Overlapped portions of the Ptpaste films 44 and 48 function as voltage-applying electrodeseffectively.

(6) Afterwards, a piezoelectric paste is, as shown in FIG. 18, printedusing a screen 43D and dried to form an unbaked preform of thepiezoelectric/electrostrictive layer 11B. One of x-direction edges ofthe unbaked preform of the piezoelectric/electrostrictive layer 11B islocated on an extension of a slant surface portion of the Pt paste film48 connecting with the Pt paste film 45. The other edge of the preformof the piezoelectric/electrostrictive layer 11B is located slightlyinside an edge of the unbaked preform of thepiezoelectric/electrostrictive layer 11A and on an extension of a slantsurface portion of the unbaked preform of thepiezoelectric/electrostrictive layer 11A.

(7) Next, a Pt paste film 49 is, as shown in FIG. 19, printed using ascreen 43E which will be a Pt paste film 49 serving as the internalelectrode layer 12B and the slant surface portion 14A of the externalelectrode layer 14 after firing and then dried. The Pt paste film 49 isopposed to the Pt paste film 48 through the unbaked preform of thepiezoelectric/electrostrictive layer 11B. The Pt paste films 48 and 49overlap each other by the distance L in the x direction.

(8) Further, a piezoelectric paste is, as shown in FIG. 20, printedusing a screen 43F which is smaller in width (length in the x direction)than the unbaked preform of the piezoelectric/electrostrictive layer 11Bserving as ground coat and then dried to form an unbaked preform of thepiezoelectric/electrostrictive layer 11C. The unbaked preform of thepiezoelectric/electrostrictive layer 11C is slightly inside an edge ofthe unbaked preform of the piezoelectric/electrostrictive layer 11Bexposed at one side from the Pt paste film 49 and the slant surfaceportion of the Pt paste film 49.

(9) Afterwards, a Pt paste film 50 is, as shown in FIG. 21, printedusing a screen 43G which serves as the internal electrode layer 12C andthe slant surface portion 15A of the external electrode layer 15 afterfiring and then dried.

(10) Next, a Pt paste is, as shown in FIG. 22, printed using a screen43H and then dried to form an unbaked preform of thepiezoelectric/electrostrictive layer 11D. The preform of thepiezoelectric/electrostrictive layer 11D is set smaller in width thanthe unbaked preform of the piezoelectric/electrostrictive layer 11Cserving as ground coat.

(11) Afterwards, a Pt paste film 51 is, as shown in FIG. 23, printedusing a screen 43I which serves as the lower surface portion 14C and theslant surface portion 14A of the external electrode layer 14 afterfiring and then dried. The screen 43I as used in this process isprovided by forming the emulsion layer 47 having a thickness of 5 μm ina given pattern on the 360 mesh metal screen 46.

(12) Finally, the temperature is increased at a rate which does notleave organic components of each material layer and the disappearingfilms 42 to perform the firing at a maximum temperature of 1100 to 1300°C., thereby causing the disappearing films 42 to disappear, as shown inFIG. 24, to allow the piezoelectric/electrostrictive elements 10 to beremoved easily from the ceramic substrate 41.

It is possible for the production method of thepiezoelectric/electrostrictive elements 10 to stack thepiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D in theprinting method so as to decrease in area gradually, thus resulting inease of manufacture of the piezoelectric/electrostrictive elements 10.It is also possible to form the piezoelectric/electrostrictive layers11A, 11B, 11C, and 11D and each electrode layer (i.e., the Pt film inthis embodiment) in the printing method, thus eliminating the need forhandling and transportation. This enables the manufacture of thepiezoelectric/electrostrictive elements 10 that are higher indimensional and positional accuracy without adverse effects such asdeformation caused by handling or transportation.

The formation of the side portions of the laminate (i.e., both sides inthe x direction) which become the continuous external electrodes isachieved by forming the piezoelectric/electrostrictive layer and theelectrode layer repeatedly, thereby eliminating the need for anadditional process of forming external electrode layers, resulting in adecrease in process.

Further, easy removal of the piezoelectric/electrostrictive elements 10after firing is achieved by forming the disappearing films 42 on theceramic substrate 41 which will disappear by the firing process prior toproducing the piezoelectric/electrostrictive elements 10. Thedisappearing films 42 disappear in the firing process by sublimation andburning, thereby preventing particles from sticking to thepiezoelectric/electrostrictive elements 10.

In the production method of the piezoelectric/electrostrictive elements,a variety of piezoelectric materials and conductive pastes that arescreen printable may be selected.

The production method of the piezoelectric/electrostrictive elementsenables the formation of the external electrode layers in the printingmethod with a higher positioning accuracy, which achieves accuratepositioning of the piezoelectric/electrostrictive elements when disposedand secured on, for example, a movable plate.

SECOND EMBODIMENT

Piezoelectric/Electrostrictive Element

FIGS. 25 and 26 show a piezoelectric/electrostrictive element accordingto the second embodiment of the invention. FIG. 25 is a side view of thepiezoelectric/electrostrictive element 60. FIG. 26 is a plan view of thepiezoelectric/electrostrictive element 60. Thepiezoelectric/electrostrictive element 60, as shown in the drawings,consists of four piezoelectric/electrostrictive layers 61, 62, 63, and64, upper surface electrode layers 65 and 66 formed at an interval awayfrom each other on an outside surface of thepiezoelectric/electrostrictive layer 61, internal electrode layers 67,68, 69, and 70 formed on lower surfaces of thepiezoelectric/electrostrictive layers 61, 62, 63, and 64, a slantsurface portion 71 leading to an upper surface electrode 65 inconnection with the internal electrode layers 68 and 70, a slant surfaceportion 72 leading to an upper surface electrode 66 in connection withthe internal electrode layers 67 and 69, and an insulating layer 73covering the slant surface portions 71 and 72 and the internal electrodelayer 70.

The piezoelectric/electrostrictive element 60 has a substantiallytrapezoidal laminated structure having a pair of opposed upper and lowerbottom surfaces of rectangular shape. The insulating layers 73 is madeof material which may be the same material as that of thepiezoelectric/electrostrictive layer 61 or different therefrom.

Both side edges of the bottom surface f2 are, as shown in FIG. 25,located inside side edges of the bottom surface f1 by equal distances,thereby forming slant surfaces f3 and f4 on both sides of thepiezoelectric/electrostrictive element 60 in the x direction. The slantsurfaces f3 and f4 are inclined in a direction in which they approacheach other from the wider bottom surface f1 to the narrower bottomsurface f2.

The upper surface electrode layer 65 is wider than the upper surfaceelectrode layer 66. The upper surface electrode layer 65 and theinternal electrode layers 68 and 70 are so formed as to extend from theslant surface portion 71 to the slant surface f4. The internal electrodelayers 67 and 69 are so formed as to extend from the slant surfaceportion 72 leading to the upper surface electrode layer 66 to the sideof the slant surface f3.

In the piezoelectric/electrostrictive element 60, areas of the uppersurface electrode layer 65 and the internal electrode layers 67, 68, 69,and 70 which overlap each other through thepiezoelectric/electrostrictive layers practically define voltage-appliedareas or voltage-detecting areas.

In the piezoelectric/electrostrictive element 60 of the secondembodiment, the bottom surface f2 and the slant surfaces f3 and f4 arecovered with the insulating layer 73. Wires leading to a voltageapplying circuit or a voltage detecting circuit are, thus, to beconnected to the upper surface electrode layers 65 and 66 of the bottomsurface f1.

In the piezoelectric/electrostrictive element 60 of the secondembodiment, the piezoelectric/electrostrictive layers 61, 62, 63, and 64are made of, for example, zirconium lead titanate (PZT). The internalelectrode layers 67, 68, 69, and 70, the upper surface electrode layers65 and 66, and the slant surface portions 71 and 72 are made of, forexample, platinum (Pt).

In the piezoelectric/electrostrictive element 60, thepiezoelectric/electrostrictive layers 61, 62, 63, and 64 laminated fromthe bottom surface f1 to the bottom surface f2 are decreased in width(length in the x direction) gradually. As a result, in the whole of thepiezoelectric/electrostrictive element 60, the slant surfaces f3 and f4are, as describe above, formed on the side portions.

In this embodiment, the piezoelectric/electrostrictive layers 61, 62,63, and 64 are four layers. The electrode layers holding thepiezoelectric/electrostrictive layers therebetween are five layers,however, the number of the layers and the number of the internalelectrode layers connecting with the slant surface portions 71 and 72may be equal to each other or not. The number of the electrode layersare determined in terms of relations to a drive voltage and the degreeof displacement. An increase in total number of thepiezoelectric/electrostrictive layers will cause a driving force drivingthe movable plate on which the piezoelectric/electrostrictive element 60is installed to be increased, thus enabling a greater displacement andresult in an increase in rigidity of the piezoelectric/electrostrictiveelement 60, thereby increasing the resonance frequency, which allows thespeed of a displacement operation to be increased easily.

Piezoelectric/Electrostrictive Device

FIG. 27 is a side view of a piezoelectric/electrostrictive device 70according to the second embodiment. The piezoelectric/electrostrictivedevice 70 is constructed to be of a unimorph type wherein the narrowerbottom surface f2 of the above described piezoelectric/electrostrictiveelement 60 is joined to a movable plate (diaphragm) 71 using adhesive72. In the piezoelectric/electrostrictive device 70 of the secondembodiment, the movable plate 71 is identical in width. The length ofthe movable plate 71 is greater than that of thepiezoelectric/electrostrictive element 60. The movable plate 71 may haveflexibility and mechanical strength which withstands breakage caused bybending. Material may be selected in terms of the response andoperationability.

In the piezoelectric/electrostrictive device 70, the adhesive 72 isinterposed between an upper surface of the movable plate 71 and a bottomsurface (lower surface f2 and the slant surfaces f3 and f4 of thepiezoelectric/electrostrictive element 60 to bond thepiezoelectric/electrostrictive element 60 on the upper surface of themovable plate 71. Particularly, V groove-shaped gaps defined between theslant surfaces f3 and f4 of the piezoelectric/electrostrictive element60 and the upper surface of the movable plate 71 are filled with theadhesive 72. As a result, the shape defined by thepiezoelectric/electrostrictive element 60 and the adhesive 72 will besubstantially trapezoidal or rectangular.

The movable plate 71 is a portion which operates based on driving of thepiezoelectric/electrostrictive element 70 and has a variety of partsinstalled thereon according to the purpose of use of thepiezoelectric/electrostrictive device 70. For instance, in a case wherethe piezoelectric/electrostrictive device 70 is used as a displacementelement, a shielding plate of an optical shutter etc. is installed. In acase where the piezoelectric/electrostrictive device 70 is employed toposition a magnetic head of a hard disc drive or in a ringing inhibitingmechanism, parts such as a magnetic head, a slider with the magnetichead, or a suspension with a slider which are required to be positionedare installed.

The movable plate 71 is a portion driven by the displacement of thepiezoelectric/electrostrictive elements 60. The movable plate 71 is aflexible member and performs a function of amplifying as a bendingdisplacement an expansion/contraction displacement of thepiezoelectric/electrostrictive elements 60 that is disposed on thesurface of the movable plate portions 71. The material of the movableplate 71 which exhibits the flexibility and mechanical strength lesssusceptible to breakage caused by the bending displacement may beselected.

As material of the movable plate 71, ceramic including zirconia isdesirable. Particularly, material containing a main component ofstabilized zirconia or partially stabilized zirconia is desirable as thematerial of the movable plate 71 because it exhibits a greatermechanical strength, a high toughness, and a small reactivity to thepiezoelectric/electrostrictive layers and an electrode material ifshaped to have a thin wall.

If the movable plate 71 is made of a metallic material, it is preferablyflexible or bendable. For example, as ferrous materials, a variety ofstainless steels or a variety of spring steels are desirable. Asnon-ferrous materials, beryllium copper, phosphor bronze, nickel, ornickel-iron alloy is desirable.

In the thus constructed piezoelectric/electrostrictive device 70, the Vgroove-shaped gaps defined by the slant surfaces f3 and f4 and the uppersurface of the movable plate 71 are formed on both sides of thepiezoelectric/electrostrictive element 70 and work as a liquid sumps forthe adhesive 72 that is liquid or pastelike. The adhesive 72 held in thegaps is solidified while being kept lump by the surface tension, therebypreventing the adhesive 72 from overflowing to or around the upper sideof the piezoelectric/electrostrictive element 60 or the lower side ofthe movable plate 71. The V groove-shaped gaps defined by the slantsurfaces f3 and f4 of the piezoelectric/electrostrictive element 60 andthe upper surface of the movable plate 71 may be filled with theadhesive 72 in proper quantities by determining the quantity of theadhesive 72 to be applied to the movable plate 71 to a predeterminedvalue.

The side corners of the lower surface f2 of thepiezoelectric/electrostrictive element 60 both have, as described above,obtuse angles, and thus have a greater strength as compared with whenthey have right angles or acute angles. The increase in strength of thecorners serves to avoid the damage or breakage of the corners caused byvibrations of the piezoelectric/electrostrictive element 60 or externalforces when the bottom surface (lower surface) f2 of thepiezoelectric/electrostrictive element 60 is secured on the movableplate 71.

Further, the stress arising from a thermal expansion difference betweenthe piezoelectric/electrostrictive element 60 and the movable plate 71is maximized near the ends of the piezoelectric/electrostrictive element60, but the adhesive 72 in the V groove-shaped gaps works to hold theadhesive strength and reduce the stress because of a low elasticity ofthe adhesive, thereby avoiding breakage and removal of the piezoelectricelement 60 from the movable plate 71.

The upper surface electrode layers 65 and 66 are arranged on the side ofthe wider bottom surface f1 (i.e., on the same plane), therebyfacilitating connection of wire to the upper surface electrode layers 65and 66.

When used as an active device, the thus constructedpiezoelectric/electrostrictive device 70 may be designed as atransducer, an actuator, a frequency domain functional part (a filter),a transformer, a vibrator or a resonator for communications or a powersource, an oscillator, or a discriminator. Wires may be providedpreferably by a flexible printed circuit (FPC), flexible flat cables(FFC), or bonding wires.

When used as a passive device, the piezoelectric/electrostrictive device70 may be designed as a ultrasonic sensor, an acceleration sensor, anangular rate sensor, a shock sensor, or a mass sensor.

In the piezoelectric/electrostrictive device 70 of the secondembodiment, the adhesive 72 sticks directly to the insulating layer 73whose surface roughness is great and which covers the bottom surface f2and the slant surfaces f3 and f4 of the piezoelectric/electrostrictiveelement 60, thus resulting in an increase in bonding strength ascompared with when the adhesive 72 sticks to a metallic electrode.

In the piezoelectric/electrostrictive device 70, by forming the uppersurface electrode layers 65 and 66 of the piezoelectric/electrostrictiveelement 60 in the printing method, the contour of the widest bottomsurface f1, patterns of the upper surface electrode layers 65 and 66 areformed precisely, thus enabling the positioning based on the uppersurface electrode layers 65 and 66. This allows thepiezoelectric/electrostrictive element 60 to be positioned accurately onthe movable plate 71.

The piezoelectric/electrostrictive device 70 of the second embodimentis, as described above, of the unimorph type, but may be of a bimorphtype.

Production Method of Piezoelectric/Electrostrictive Device

A production method of a piezoelectric/electrostrictive device which maybe employed with the first and second embodiments will be describedbelow using FIGS. 28 to 33. The method includes the following steps A-E.

(A) First, a movable plate 80, as shown in FIG. 28, is prepared. Anadhesive 81 is, as shown in FIG. 29, applied to a given position of themovable plate 80 using the screen printing method.

(B) Next, the movable plate 80 is, as shown in FIGS. 30 and 31, put on amovable plate positioning jig 82. The movable plate positioning jig 82has a pair of guide pins 84 installed on side portions of a movableplate positioning substrate 83. Three vertically extending positioningpins 35 are installed on a central portion of the movable platepositioning substrate 83 in engagement with two sides of the movableplate 80.

(C) The piezoelectric/electrostrictive element 10 is set on an elementpositioning plate 86. The element positioning plate 86 has formedtherein a plurality of vacuum openings 87 for fixing in place thepiezoelectric/electrostrictive element 10 by use of suction. Thepiezoelectric/electrostrictive element 10 is set so that the widerbottom surface f1 may be fixed in place by the suction of vacuumopenings 87. The element positioning plate 86 has formed therein guideholes 88 in which guide pins 84 are fitted when combined with themovable plate positioning jig 82. The element positioning plate 86 hasalso formed therein openings 89 for reception of the positioning pins 35installed on the movable plate positioning jig 82.

(D) The guide pins 84 of the movable plate positioning jig 82 are, asshown in FIG. 33, inserted into the guide holes 88 of the elementpositioning plate 86. The element positioning plate 86 is brought closeto the movable plate positioning jig 82 to bring thepiezoelectric/electrostrictive element 10 into contact with the movableplate 80 disposed on the movable plate positioning jig 82, therebycausing the piezoelectric/electrostrictive element 10 to be bonded andsecured by the adhesive 81 applied to the movable plate 80.

(E) Afterwards, the suction by the vacuum openings 87 of the elementpositioning plate 86 is stopped. The element positioning plate 86 isthen lifted upward to terminate the positioning of thepiezoelectric/electrostrictive element 10.

Afterwards, a weight is put on the piezoelectric/electrostrictiveelement 10 to hold it from moving during solidification of the adhesive.For example, in a case of a thermosetting one-component epoxy resinadhesive, it is put in an oven heated up to a solidifying temperature.In a case of a UV cured adhesive, an ultraviolet ray is radiated tosolidify the bond.

In the above described piezoelectric/electrostrictive device productionmethod, the piezoelectric/electrostrictive element 10 is bonded to oneof the surfaces of the movable plate 80. In a case where thepiezoelectric/electrostrictive elements 10 are bonded to the surfaces ofthe movable plate 80, the piezoelectric/electrostrictive element 10 isadhered to one of the surfaces of the movable plate 80 in the abovemanner, after which another movable plate positioning jig is preparedwhich is designed to be disposed on the movable plate 80 that is turnedover to bond the piezoelectric/electrostrictive element 10 to thereverse surface.

In the above piezoelectric/electrostrictive device production method,proper bonding may be carried out in a proper quantity of the adhesive81, as shown in FIG. 5, by determining the quantity and thickness of theadhesive 81 to be applied to the movable plate 80 to predeterminedvalues. It is possible to control an applied position and an appliedquantity of adhesive accurately, depending upon physical properties (thecoefficient of viscosity or thixotropy). Thus, as an application methodof the adhesive, the screen printing method is preferably used.

Other Embodiments

It should be noted that the discussion and the drawings that are partsof the disclosure of the above described first and second embodiments ofthe invention do not limit the invention. From this disclosure, oneskilled in the art will know alternative various forms of embodiments,and working techniques.

For instance, the first and second embodiments refer to the cases wherethe number of the inner electrode layers are three and four, but may beone, two or more, or five or more.

When produced by the printing method, the piezoelectric/electrostrictiveelements 10 and 60 have advantages of production, dimensional accuracy,and positional accuracy, but even if the piezoelectric/electrostrictiveelements 10 and 60 are not produced by the printing method, they mayhave the advantage of strength as long as at least the corners of theside portions of the bottom surface have obtuse angles.

In the above described first and second embodiments, the adhesive is putin the V groove-shaped gaps defined by thepiezoelectric/electrostrictive element and the movable plate. Theinvention may also be used in the case where only the narrower bottomsurface is bonded by adhesive.

1-23. (Canceled).
 24. A method of producing apiezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes, and the piezoelectric/electrostrictiveelement is bonded to a surface of a movable plate by adhesive.
 25. Amethod of producing a piezoelectric/electrostrictive device as set forthin claim 24, wherein said piezoelectric/electrostrictive elements arebonded to surfaces of said movable plate through adhesive.
 26. A methodof producing a piezoelectric/electrostrictive device in which a pair ofpiezoelectric/electrostrictive elements each include a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes, and the piezoelectric/electrostrictiveelements are bonded to each other on sides of the respective narrowersurfaces of said laminates through adhesive.